The makeshift message boards represent claims of credit for the ghastly images that follow: children, some pleading for help, being sexually abused in torturous ways by parents, relatives or others. Among the worst: infants used as toys for the videographers' and viewers' sexual gratification.

The cache of images are among the most vile, yet valued, commodities on what is known as the "dark Web.'' It is an ever-expanding part of the Internet where Drew Oosterbaan, chief of the Justice Department's unit investigating crimes against children, says purveyors of the material have found social status based on their continued and escalating activities.

Last year, more suspects were arrested for child exploitation crimes - 7,386 - than at any time in the past five years, according to Justice Department records gathered from 61 Internet Crimes Against Children task forces across the nation.

That number, however, is dwarfed by an estimated 50,000 people in the U.S. who are believed to be "consistently trading illegal images'' involving children at any time, says Brad Russ, who oversees federally funded training programs for hundreds of investigators assigned to the national task forces. The enormous number of participants, Russ says, is based on the downloads of known prohibited videos and photographs that can be tracked to individual computers.

The universe of known images has ballooned since 2002, the year of the creation of the Child Victim Identification Program, which serves as a national repository for information on young victims, says John Shehan, executive director of the Exploited Children Division at the National Center for Missing & Exploited Children (NCMEC).

More than 100 million images and videos of suspected child abuse have been referred to the program housed within NCMEC to assist in criminal investigations and for the purpose of locating child victims, Shehan says.

"It is alarming,'' Russ said of the numbers, adding that suspects increasingly try to shield their activities from law enforcement.

They cloister themselves behind encrypted IP addresses and password-protected sites where they have found "validation, acceptance and encouragement'' to find new victims, Oosterbaan says.

"I signed up ... because I feel at home here,'' one suspected pedophile wrote to fellow members of a notorious child pornography clearinghouse in a message recovered by federal authorities. "I am a pedophile and I have been sexually attracted to children rather than adults for 30 years now. My life is pretty lonely because I have no friends who are like me where I live. That's why I'm happiest when I am ... with people just like me. Thank you for the company, my fellow friends. Keep safe and may God bless you.''

A separate suspect posted a sonogram photograph of an unborn child, along with the message: "I have a new baby about to be added to the game.''

SUPPLY AND DEMAND

When criminal charges were announced against 11 men last November in Indianapolis, the case represented a significant break in a suspected long-running child pornography ring. It also underscored the daunting challenges now facing investigators who police the dark Web.

For at least 12 years, federal prosecutors say, the 11 suspects, operating from bases in Indiana, Florida, California, Alabama, New York, Texas and Virginia, ran online chat-rooms where huge collections of child pornography were shared among members, representing Canada, Switzerland and other parts of the globe.

Before their arrests, according to court documents, the suspects found temporary havens protected by "data encryption software'' and password-protected sites "available exclusively to members of the conspiracy.''

"This conspiracy allegedly stretched across the country and around the world, using sophisticated techniques to hide the orchestrated abuse of dozens of child victims,'' Indiana U.S. Attorney Joseph Hogsett said when the charges were made public.

In fact, after all of the image caches were recovered, federal authorities said the number of victims numbered "nearly 100 children around the world'' whose ages ranged from infants to early teens, according to court documents.

One of the defendants, a 61-year-old Indianapolis man, already has been sentenced to 17.5 years in federal prison. Eight have agreed to plead guilty and are awaiting sentencing. Two others, a 42-year-old Florida man and a 55-year-old Alabama man, are awaiting trial.

The case bears the hallmarks - including the extremely young nature of the victims and growing masses of material - that have become the norm in recent investigations.

"What I've seen is an evolution in the intensity and volume of their conduct,'' Oosterbaan says. "There is a greater demand for extreme material. ... For some, their social status is based on production (of new images), which serves as a powerful stimulus for the actual abuse of children.''

Law enforcement authorities and child safety advocates say it is difficult to quantify the size of the illicit commercial market for child pornography and the access it brings to actual encounters with children. While some of it is produced for profit, others provide it as a form of status or to win acceptance within groups.

"There is a commercial incentive for some of this,'' Oosterbaan says, adding that he would not be comfortable assigning a dollar value to it.

Shehan, of NCMEC, says that while the identification and arrest of the image-makers and distributors is important, it is only the beginning of an even more time-consuming - and often frustrating - effort to locate the victims featured in the images and videos.

"When you finally recover the material, you are always left with the same question: Where in the world are these children?'' Shehan says.

Since the creation of the Child Victim Identification Program 12 years ago, 5,400 victims have been identified. The number, Shehan says, may represent only a fraction of the actual number.

"There could be thousands of others that we're still looking for,'' he says.

CYBER-POLICING TOOLS

Among the most powerful tools law enforcement is using to break distribution rings and start the tracking of child victims is software that allows authorities to virtually map the locations of suspects.

The technology, known as ICAC (Internet Crimes Against Children) Cops, tracks the coding of images recovered in previous investigative operations that have been downloaded to individual computers.

During a recent demonstration of the technology, authorities were able to zero in on suspects who are actively downloading material in their local jurisdictions at any time of day or night.

One recent afternoon, the locations of possible suspects were depicted by icons blinking like warning lights across a large computer screen, from Scranton, Pa., to Los Angeles.

In Pennsylvania, for example, the online activity linked to the suspected transmission of child pornography and/or solicitations for sexual encounters involved more than 2,000 individuals.

And of the 114 arrests of porn distribution suspects in Pennsylvania last year by state authorities, the technology aided in the identification of about 80% of them, officials said.

"It is one of the most effective tools available to law enforcement,'' Russ says.

Russ says one of the least-discussed challenges that authorities are confronting is the emotional toll that prolonged exposure to the horrific images can exact on investigators involved in the daily pursuit of offenders and victims.

Of the hundreds Russ has helped train, "I don't know how many are still out there,'' he says.

Oosterbaan, too, acknowledges the emotional damage that some investigators risk.

"There is real courage here,'' the Justice official says, motioning to the staff of investigators ensconced in a warren of offices located on the sixth floor of a downtown office building a few blocks away from the Justice Department. "I worry about it.''

So concerned about the potential emotional harm, he once planned to withhold graphic images from Alberto Gonzales when the then-attorney general requested a full briefing on the unit's operations in 2005.

Oosterbaan ultimately relented when Gonzales' aides persisted. Later, Rebecca Gonzales, the attorney general's wife, recalled in an interview that the nation's top law enforcement officer arrived home shaken after the briefing.

"He didn't cry, but it was close," she says. "That was a terrible day.''

When Oosterbaan took over the unit in 2002, he took unusual care to protect himself.

"There are many ways you can protect yourself and one of the ways I can is not to look,'' he says of the very images that represent some of the strongest evidence in criminal cases that his office oversees. The official says he opts instead for verbal briefings on the cases his office prosecutes.